The focus of this project was to describe the sequelae of biochemical and molecular events regulating cAMP levels in the rat pineal gland following the termination of Beta-receptor stimulation. Initial experiments were conducted on fresh pineal glands in culture medium. Results showed an apparent translocation of calmodulin from membrane fraction to the cytosol in response to Beta-receptor blockage. In cultured cells maximal response (2-fold increase) was within 10 minutes. Termination of Beta-receptor stimulation could also be accomplished in vivo by exposing dark-adapted animals to light. Under this paradigm, a number of rapidly occurring events were observed: (1) Two-fold increase in cytosol calmodulin within 1 minute and return to control levels within 2 minutes; (2) activation of PDE within 1 minute and then a decrease in activity below control values at 2 minutes and (3) decrease in cAMP levels at 1 minute, then a 2 to 3-fold increase from control levels at 4 and 6 minutes. Present results outline a number of rapidly and possibly interrelated series of biochemical events in the pineal gland in response to termination of Beta-receptor stimulation.